I think you have the outside grommet on upside down. You might like the fit a little better the other way. There should also be an inside grommet to help hold things firm. I can't tell from the pics if it is there or not. Nick, the truck is looking good and you are knocking things off the list! It has to feel good.
1947.2 GMC 1/2T SWB panel 1947.2 GMC 1/2T long bed 1948 GMC 1/2T short bed